1. Field of the Invention
The present invention relates generally to a protective cover adapted to be externally fitted onto components such as shock absorbers of automotive suspensions, robot arms, or the like, which are to be permitted extension/contraction or bend, and prevent adhesion of water, dust, or other foreign matters to the components. The present invention also relates to a manufacturing method of the same.
2. Description of the Related Art
Conventionally, tubular protective covers (dust covers) are generally externally fitted onto shock absorbers of automotive suspensions, robot arms, or the like serving as components to be attached, in order to permit extension/contraction or bend while preventing adhesion of water, grit, or other foreign matters. The protective cover includes, in at least a portion thereof, a bellows portion having peaks and valleys formed in continuous fashion, and is endowed with elasticity in the axial direction owing to deformation of the bellows portion. Japanese Examined Utility Model Publication No. JP-Y-4-973 discloses one example thereof.
Meanwhile, it is desirable for the protective cover to have a sufficiently large extension/contraction stroke (differential between the axial dimension during extension and the axial dimension during contraction) in order to ensure followability to the extension/contraction or bend of the components to be attached.
Thus, in order to obtain a small axial dimension during contraction, the protective cover described in JP-Y-4-973 proposes a structure in which large valleys and small valleys are alternately arranged in an alternating sequence so that the small valleys are wrapped by the large valleys during contraction.
However, the protective cover described in JP-Y-4-973 sometimes finds it difficult to ensure sufficient elasticity and the required extension/contraction stroke may not be achieved. Specifically, with the protective cover in which the large valleys and the small valley are just alternately formed, if the depth (D) of the small valleys is made small in order to obtain a small axial dimension during contraction, the axial dimension during extension is likely to be insufficient. On the other hand, if the depth of the small valleys is made large in order to obtain a large axial dimension during extension, the inner peripheral edges of the small valleys are positioned in the vicinity of the inner peripheral edges of the large valleys so that the axial dimension during contraction is likely to be large, making it difficult to ensure a sufficient extension/contraction stroke.